1. Field of the Invention
This invention relates to a power drive unit, more specifically to a power drive unit equipped with power modules that are pressed by a press member to a heat sink to be fastened thereto.
2. Description of the Related Art
The hybrid vehicle that has emerged in various forms in recent years is equipped with an internal combustion engine, electric motor(s), battery or other such energy storage device, and the like. During driving of the hybrid vehicle, the engine and motor(s) are controlled in response to the driving or running conditions of the vehicle (e.g., whether the vehicle drives at high speed or low speed). The electric motor used in such a hybrid vehicle constitutes, for example, a brushless DC motor and is operated by forwarding direct current to U, V and W-phases of its stator from a power drive unit (PDU), more exactly from power modules in the PDU.
Japanese Laid-Open Patent Application No. 2004-87552 especially paragraphs 0008, 0009 and FIG. 1 etc.) teaches an example of a power drive unit in which a spring member of a pent-roof shape viewed in cross-section is installed on one side of a power module that is bored with a screw inserting hole, and a screw is inserted into the screw inserting hole through the spring member to, while pressing, fasten the power module to a heat sink.
However, the configuration to provide the screw inserting hole in the power module as in the prior art causes limitation in layout of electronic components, such as an IGBT (Insulated-Gate Bipolar Transistor) and diode, constituting the power module. Also, since a contact area between the power module and the heat sink decreases by a portion of the screw inserting hole, heat release performance of the power module disadvantageously lowers.